Recently, as information and communication technology rapidly develops, a ubiquitous society based on information and communication technology is being formed.
In order for information communication devices to be connected anywhere and anytime, sensors equipped with a computer chip having a communication function should be installed in all facilities throughout the society. Accordingly, power supply to these devices or sensors is becoming a new challenge. In addition, as the types of mobile devices such as Bluetooth handsets and iPods, as well as mobile phones, rapidly increase in number, charging the battery has required time and effort for users. As a way to address this issue, wireless power transmission technology has recently drawn attention.
Wireless power transmission (or wireless energy transfer) is a technology for wirelessly transmitting electric energy from a transmitter to a receiver using the induction principle of a magnetic field. Back in the 1800s, an electric motor or a transformer based on the electromagnetic induction principle began to be used. Thereafter, a method of transmitting electric energy by radiating an electromagnetic wave such as a radio wave or laser was tried. Electric toothbrushes and some wireless shavers are charged through electromagnetic induction.
Up to now, wireless energy transmission schemes may be broadly classified into electromagnetic induction, electromagnetic resonance, and RF transmission using a short-wavelength radio frequency.
In the electromagnetic induction scheme, when two coils are arranged adjacent to each other and a current is applied to one of the coils, a magnetic flux generated at this time generates an electromotive force in the other coil. This technology is being rapidly commercialized mainly for small devices such as mobile phones. In the electromagnetic induction scheme, power of up to several hundred kilowatts (kW) may be transmitted with high efficiency, but the maximum transmission distance is within 1 cm. As a result, the device should be generally arranged adjacent to the charger or the floor.
The electromagnetic resonance scheme uses an electric field or a magnetic field instead of using an electromagnetic wave or current. The electromagnetic resonance scheme is advantageous in that the scheme is safe to other electronic devices or the human body since it is hardly influenced by the electromagnetic wave. However, this scheme may be used only at a limited distance and in a limited space, and has somewhat low energy transfer efficiency.
The short-wavelength wireless power transmission scheme (simply, RF transmission scheme) takes advantage of the fact that energy can be transmitted and received directly in the form of radio waves. This technology is an RF power transmission scheme using a rectenna. A rectena, which is a compound of antenna and rectifier, refers to a device that converts RF power directly into direct current (DC) power. That is, the RF method is a technology for converting AC radio waves into DC waves. Recently, with improvement in efficiency, commercialization of RF technology has been actively researched.
Wireless power transmission technology may be applied to various industries including IT, railroad, and home appliance industries as well as the mobile industry.
Particularly, in recent years, research on a wireless power transmission device and a wireless power reception device that support a plurality of wireless power transmission schemes has been actively conducted.
For a wireless power transmission device supporting both the electromagnetic induction scheme and the electromagnetic resonance scheme, since a transmission induction coil and a transmission resonant coil are positioned on the same charging bed (or charging pad), mutual interference may be caused by the coupling effect, and accordingly power loss may occur.